Impact of recombinant baculovirus field applications on a nontarget heliothine parasitoid, Microplitis croceipes (Hymenoptera : Braconidae)

The kill times of two viruses infectious to the heliothine pest complex ind igenous to Texas cotton have been significantly reduced Lp expressing a sco rpion toxin gene. Autographa californica nucleopolyhedrovirus us (NPV) and Helicoverpa zea NPV express the toxin only in per missive lepidopteran host s. The toxin, however, could indirectly harm members of upper trophic level s that feed upon and parasitize infected larvae producing the toxin. In thi s study, the effects of recombinant and wild-type viruses on Microplitis cr oceipes (Cresson) were studied in cotton using Heliothis virescens (F.) (Le pidoptera: Noctuidae) as hosts. Two recombinant viruses, their two wild-typ e progenitor viruses, and untreated cotton served as the five treatments of study. Larvae were previously parasitized 2 and Id before being confined f or 72 h to cotton terminals treated with field rates of virus or left untre ated. The sexes of adult hi. croceipes that emerged fr om the recovered Ii. virescens larvae were determined and their tread capsule widths were measu red. Polymerase chain reaction (PCR) searched their extracts for virus DNA. There were no differences in percentage emergence and sex ratios of parasi toids among recombinant, wild-type, and control treatments. Significantly m ore wasps emerged from the 4-d cohort, but these wasps were significantly s maller than wasps from the 2-d cohort regardless of treatment. Finally, PCR found only 15-25% of the recovered H. virescens larvae and none of the eme rgent M croceipes had detectable levels of viral DNA. Recombinant and wild- type viruses had a similar, minimal impact on emergent wasps, and the proba bility of virus dispersal via parasitoids is low in the system tested.